Automatic detection and application of editing patterns in draft documents

ABSTRACT

An error detection and correction system extracts editing patterns and derives correction rules from them by observing differences between draft documents and corresponding edited documents, and/or by observing editing operations performed on the draft documents to produce the edited documents. The system develops classifiers that partition the space of all possible contexts into equivalence classes and assigns one or more correction rules to each such class). Once the system has been trained, it may be used to detect and (optionally) correct errors in new draft documents. When presented with a draft document, the system identifies first content (e.g., text) in the draft document and identifies a context of the first content. The system identifies a correction rule based on the first content and the first context. The system may use a classifier to identify the correction rule. The system applies the correction rule to the first content to produce second content.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to the following commonly-owned U.S. patentapplications, hereby incorporated by reference:

U.S. patent application Ser. No. 10/923,517, filed on Aug. 20, 2004,entitled, “Automated Extraction of Semantic Content and Generation of aStructured Document from Speech”; and

U.S. patent application Ser. No. 10/922,513, filed on Aug. 20, 2004,entitled, “Document Transcription System Training.”

BACKGROUND

1. Field of the Invention

The present invention relates to editing documents and, moreparticularly, to detecting and correcting errors in draft documentsproduced using an automatic document transcription system or othermeans.

2. Related Art

It is desirable in many contexts to generate a structured textualdocument based on human speech. In the legal profession, for example,transcriptionists transcribe testimony given in court proceedings and indepositions to produce a written transcript of the testimony. Similarly,in the medical profession, transcripts are produced of diagnoses,prognoses, prescriptions, and other information dictated by doctors andother medical professionals. Transcripts in these and other fieldstypically need to be highly accurate (as measured in terms of the degreeof correspondence between the semantic content (meaning) of the originalspeech and the semantic content of the resulting transcript) because ofthe reliance placed on the resulting transcripts and the harm that couldresult from an inaccuracy (such as providing an incorrect prescriptiondrug to a patient). It may be difficult to produce an initial transcriptthat is highly accurate for a variety of reasons, such as variations in:(1) features of the speakers whose speech is transcribed (e.g., accent,volume, dialect, speed); (2) external conditions (e.g., backgroundnoise); (3) the transcriptionist or transcription system (e.g.,imperfect hearing or audio capture capabilities, imperfect understandingof language); or (4) the recording/transmission medium (e.g., paper,analog audio tape, analog telephone network, compression algorithmsapplied in digital telephone networks, and noises/artifacts due to cellphone channels).

The first draft of a transcript, whether produced by a humantranscriptionist or an automated speech recognition system, maytherefore include a variety of errors. Typically it is necessary toproofread and edit such draft documents to correct the errors containedtherein. Transcription errors that need correction may include, forexample, any of the following: missing words or word sequences;excessive wording; mis-spelled, -typed, or -recognized words; missing orexcessive punctuation; and incorrect document structure (such asincorrect, missing, or redundant sections, enumerations, paragraphs, orlists).

Furthermore, formatting requirements may make it necessary to edit evenphrases that have been transcribed correctly so that such phrases complywith the formatting requirements. For example, abbreviations andacronyms may need to be fully spelled out. This is one example of a kindof “editing pattern” that may need to be applied even in the absence ofa transcription error.

Such error correction is typically performed by human proofreaders andcan be tedious, time-consuming, costly, and itself error-prone.Furthermore, many error patterns occur frequently across documents andthe necessity to repeatedly correct them may create a significant levelof discontent among proofreaders. What is needed, therefore, areimproved techniques for correcting errors in draft documents.

SUMMARY

An error detection and correction system extracts editing patterns andderives correction rules from them by observing differences betweendraft documents and corresponding edited documents, and/or by observingediting operations performed on the draft documents to produce theedited documents. The system develops classifiers that partition thespace of all possible contexts into equivalence classes and assigns oneor more correction rules to each such class). Once the system has beentrained, it may be used to detect and (optionally) correct errors in newdraft documents. When presented with a draft document, the systemidentifies first content (e.g., text) in the draft document andidentifies a context of the first content. The system identifies acorrection rule based on the first content and the first context. Thesystem may use a classifier to identify the correction rule. The systemapplies the correction rule to the first content to-produce secondcontent.

For example, in one aspect of the present invention, acomputer-implemented method is provided that includes steps of: (A)identifying a plurality of editing patterns of the form T=(D,E,C),wherein each of the plurality of editing patterns relates particularcontent D in an original document corpus to corresponding content E inan edited document corpus in a context C shared by contents D and E; and(B) deriving at least one correction rule from the plurality of editingpatterns.

In another aspect of the present invention, a computer-implementedmethod is provided for editing a first document. The method includessteps of: (A) identifying first content in the document; (B) identifyinga first context of the first content; (C) identifying a correction rulebased on the first content and the first context; and (D) applying thecorrection rule to the first content to produce second content.

In yet another aspect of the present invention, a computer-implementedmethod is provided for editing a document. The method includes steps of:(A) identifying first content in the document; (B) identifying a firstcontext of the first content; (C) determining whether a classifierapplicable to the first content exists in a predetermined set ofclassifiers; and (D) if the classifier exists, performing steps of:(D)(1) using the classifier to identify a correction rule applicable tothe first content in the first context; and (D)(2) applying theidentified correction rule to the first content to produce secondcontent.

Other features and advantages of various aspects and embodiments of thepresent invention will become apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a dataflow diagram of a system for training a document errordetection and correction system according to one embodiment of thepresent invention;

FIG. 2A is a flowchart of a method performed by the system of FIG. 1Aaccording to one embodiment of the present invention;

FIG. 1B is a dataflow diagram of another embodiment of the documenterror detection and correction system of FIG. 1A;

FIG. 2B is a flowchart of a method that is performed by the system ofFIG. 1B in one embodiment of the present invention;

FIGS. 3A-3B are flowcharts of methods for generating editing patternsaccording to various embodiments of the present invention;

FIG. 4 is a flowchart of a method that is performed by the correctionrule generator of FIGS. 1A-1B to, generate correction rules according toone embodiment of the present invention;

FIG. 5 is a flowchart of a method for generating classifiers accordingto one embodiment of the present invention;

FIG. 6 is a flowchart of a high-level method performed by variousembodiments of the present invention to correct errors by applyingcorrection rules that are selected based on the contexts of the contentto which they are applied;

FIG. 7 is a dataflow diagram of a system for detecting and correctingerrors using a document correction system that includes the correctionrules and the classifiers of FIGS. 1A-1B;

FIG. 8 is a flowchart of a method performed by the system of FIG. 7 todetect and correct errors in draft documents according to one embodimentof the present invention; and

FIGS. 9A-9B are diagrams illustrating a space of possible contexts for aparticular content according to one embodiment of the present invention.

DETAILED DESCRIPTION

Embodiments of the present invention are directed to techniques fordetecting and correcting errors in draft documents. An error detectionand correction system is trained by enabling the system to: (1) detectdifferences between draft documents and corresponding edited versions ofsuch documents; and/or (2) observe the editing operations that areperformed on the draft documents to correct errors therein. Using eithertraining method, the system extracts a set of editing patterns thatrelate particular document content (such as text) in a particularcontext in a draft document to the corresponding edited content in thecorresponding-edited document. The system may use such editing patternsto develop: (1) correction rules that map draft content to editedcontent, (2) classifiers that may be used to identify the correctionrule to apply to subsequently-observed content based on the context ofsuch content; and (3) a classification of editing patterns into a set ofcategories that indicate, for example, the source of or reason for theediting pattern (e.g. punctuation-related, capitalization-related,hyphenation-related, formatting operation, general wordsubstitution/deletion/insertion).

Once the system has been trained, it may be used to detect and correcterrors in new documents, such as literal or non-literal transcripts ofspeech produced by a human transcriptionist or an automatedtranscription system. When presented with a new draft document, thesystem identifies any content for which correction rules exist. For eachsuch content, the system uses one or more classifiers to select acorrection rule to apply to the content based on the context of thecontent. The system applies the selected correction rule to the content,thereby producing edited content. In this way the system attempts tocorrect errors in the draft document.

The system may allow the user to select a correction rule, such as byallowing the user to select an edited version of the content from a listof candidate edited contents produced by competing correction rules. Theuser may then specify the correction rule to apply by selecting one ofthe candidate edited contents from the list.

Referring to FIG. 1A, a dataflow diagram is shown of a system 100 a fortraining a document error detection and correction system according toone embodiment of the present invention. Referring to FIG. 2A, aflowchart is shown of a method 200 performed by the system 100 a of FIG.1A according to one embodiment of the present invention. A transcriptionsystem 104 transcribes a spoken audio stream 102 to produce a drafttranscript 106 (step 202). The spoken audio stream 102 may, for example,be dictation by a doctor describing a patient visit. The spoken audiostream 102 may take any form. For example, it may be a live audio streamreceived directly or indirectly (such as over a telephone or IPconnection), or an audio stream recorded on any medium and in anyformat.

The transcription system 104 may produce the draft transcript 106 usinga human transcriptionist, an automated speech recognizer, or anycombination thereof. The transcription system 104 may, for example,produce the draft transcript 106 using any of the techniques disclosedin the above-referenced patent application entitled “AutomatedExtraction of Semantic Content and Generation of a Structured Documentfrom Speech.” As described therein, the draft transcript 106 may beeither a literal (verbatim) transcript or a non-literal transcript ofthe spoken audio stream 102. As further described therein, although thedraft transcript 106 may be a plain text document, the draft transcript106 may also, for example, be a structured document, such as an XMLdocument which delineates document sections and other kinds of documentstructure.

An editing system 108 performs editing operations on the drafttranscript 106 to produce an edited transcript 110 (step 204). Theediting system 108 may, for example, include a human editor who editsthe draft transcript 106 in an attempt to correct errors therein. Theediting system 108 may also include, for example, conventional errorcorrection means such as a conventional automatic spelling correctionsystem. Editing operations that may be performed by the editing system108 include, for example, adding content, deleting content, and movingcontent.

In the embodiment illustrated in FIGS. 1A and 2A, an editing patternidentifier 112a identifies editing patterns 114 a based on differencesbetween the draft transcript 106 and the edited transcript 110 (step 206a). The editing pattern identifier 112 a may, for example, attempt toalign the-draft transcript 106 with the edited transcript 110. Documentalignment may be performed from the structural level down to theindividual word level, with the assumption that document structure ispreserved during editing. The alignment attempt will reveal differencesbetween the draft transcript 106 and the edited transcript 110. Forexample, text that appears at a particular location in the drafttranscript 106 but not at the same location in the edited transcript 110indicates that the editing system 108 deleted the text from the drafttranscript 106 when producing the edited transcript 110.

As noted above, the draft transcript 106 and edited transcript 110 maybe structured documents containing not only plain text but also documentstructures representing semantic and syntactic concepts, as those termsare defined in the above-referenced patent application entitled“Automated Extraction of Semantic Content and Generation of a StructuredDocument from Speech.” As described in more detail therein, the term“concept” includes, for example, dates, times, numbers, codes,medications, medical history, diagnoses, prescriptions, phrases,enumerations and section cues. The term “content” is used herein torefer generally to any subset of a document, which may therefore includenot only plain text but also representations of one or more concepts.The alignment performed by the editing pattern identifier 112 a may,therefore, reveal editing not only of text, but also editing (e.g.,addition, deletion, or movement) of document structures.

As used herein, the term “editing pattern” refers to a relationshipbetween first content D in a first document (such as the drafttranscript 106) and second content E in a second document (such as theedited transcript 110) in a particular shared context C. As used herein,the “context” of some content D is defined as any set of facts,circumstances, or features that relate to a document containing contentD and that assist in interpreting content D. One example of the contextof a particular unit of content D is the content (e.g., words) thatimmediately precedes and follows the content in the document. Forexample, in the case of the text “Patient John Smith,” the words“Patient” and “Smith” would be an example of context for the word“John.” This example of context may be generalized to include any amountof content preceding and following particular content.

Other examples of context for content D include: (1) the type of speechof content D (e.g., noun or verb) and/or of the words preceding andfollowing content D; (2) the section (or other document structure)within which content D appears; (3) the domain or worktype (examples ofwhich include letter, discharge summary, progress note, consultationnote, discharge summary, or radiology report in the context of medicalreports) of the document in which content D appears; and (4) theidentity of the documents author or editor. Note that these are merelyexamples of the kinds of contexts that the editing pattern identifier112 a may be configured to utilize when generating editing patterns.

In the following description, an editing pattern T will be indicatedusing the notation T=(D,E,C), where D is content in a first document(e.g., the draft transcript 106), E is corresponding content in a seconddocument (e.g., the edited transcript 110), and C is the shared contextin which D and E appear in their respective documents. Note that contextC does not necessarily uniquely determine the pair,D and E in thedocument. Note further that either D or E (but not both) may be empty,thereby representing content insertion (when D is empty) or deletion(when E is empty). Such an editing pattern is referred to as a “positivepattern” if D differs from E. In step 206 a, the editing patternidentifier 112 a may identify one or more positive editing patterns bycomparing the draft transcript 106 to the edited transcript 110 andproduce a positive editing pattern for each content D in the drafttranscript 106 and content E in the edited transcript 110 if and only ifD differs from E and both D and E occur in the same context C. Eachediting pattern T=(D,E,C) may occur one or more times in a collection ofdocument pairs. An occurrence count N may therefore be associated witheach editing pattern.

A correction rule generator 116 derives correction rules 118 from theediting patterns 114 a (step 208). As used herein, the term “correctionrule” refers to a rule R=(D,E), which indicates that content D is to bereplaced (e.g., corrected) with content E. The correction rule (D,E)may, for example, be derived in step 208 from the editing pattern(D,E,C) . As will be described in more detail below, the correctionrules 118 may subsequently be used to correct errors in other documents.

A classifier generator 120 uses an induction algorithm to deriveclassifiers 122 for selecting the correction rule to apply tosubsequently-observed content based on the context of such content (step210). In general, a classifier partitions the space of all possiblecontexts for particular content D into equivalence classes based on theediting patterns observed in a training set, such that each equivalenceclass corresponds to a unique correction rule (D,E) . Examples oftechniques for generating the classifiers 122 will be described in moredetail below with respect to FIG. 5.

Note that although the correction rules 118 and classifiers 122 areshown in FIGS. 1A and 2A as being generated in separate steps (208 and210) by separate components (116 and 120), this is not a requirement ofthe present invention. As will be described in more detail below, thecorrection rules 118 and classifiers 122 are interrelated and may begenerated in an integrated process by a combined rule/classifiergenerator.

Referring to FIG. 1B, a dataflow diagram is shown of another embodiment100 b of the document error detection and correction system 100 a.Referring to FIG. 2B, a flowchart is shown of a method 220 that isperformed by the system 100 b in one embodiment of the presentinvention. Like the system 100 b shown in FIG. 1A, the system 100 bshown in FIG. 1B includes transcription system 104 for transcribing thespoken audio stream 102 into the draft transcript 106 (steps 202-204).Recall that the editing pattern identifier 112 a in FIG. 1A produced theediting patterns 114 a based on observed differences between the drafttranscript 106 and the edited transcript 110. In contrast, the editingpattern identifier 112 b system in FIG. 1B generates editing patterns114 b by observing the performance of editing operations 130 a-cperformed on the draft transcript 106 to produce the edited transcript110 (step 206b). The editing pattern identifier 112 b may, for example,monitor the keypresses, mouseclicks, and other input received from auser while editing the draft transcript. The editing pattern identifier112 b may record information such as the kind of input (e.g., keypressor mouse click), identifying features of the input (e.g., the identityof the key pressed or the coordinates and type of mouse click), and thecontext in which the input is received (e.g., the characters surroundingthe location of the text cursor at the time the input is received).Editing operation 130 a produces an intermediate edited draft transcript132 a, editing operation 130 b produces an intermediate edited drafttranscript 132 b, and editing operation 130 c produces the final editedtranscript 110. Although only three editing operations 130 a-c are shownin FIG. 1B, any number of editing operations may be performed andmonitored.

The method 220 concludes by deriving the correction rules 118 from theediting patterns 114 b and generating the classifiers 122 based on theediting patterns 114 b in the manner described above with respect toFIGS. 1A and 2A. The methods shown in FIGS. 1A and 2A may be combinedwith those shown in FIGS. 1B and 2B to train the system using bothobserved differences between documents and observed editing operations.

As mentioned above, the editing pattern identifiers 112 a-b (referred toherein collectively as editing pattern identifier 112) may identify oneor more editing patterns by comparing the draft transcript 106 to theedited transcript 110 and producing a positive editing pattern for eachcontent D in the draft transcript 106 that occurs in the same context Cas different content E in the edited transcript 110. Referring to FIG.3A, a flowchart is shown of a method 300 that may be performed by theediting pattern identifier 112 to generate such positive editingpatterns.

The method 300 enters a loop over each unit of content D in the drafttranscript 106. If the draft transcript 106 is a flat text document, theunits of content may, for example, be sequences of one or moreconsecutive words. If the draft transcript 106 is a structured document,the units of content may additionally include, for example, paragraphs,sections, dates, or other kinds of “concepts” as that term is defined inthe above-referenced patent application entitled “Automated Extractionof Semantic Content and Generation of a Structured Document fromSpeech.” If the draft transcript 106 is a hierarchical structureddocument, the method 300 may iterate over contents in the drafttranscript 106 by navigating the hierarchy of the document, in whichcase the contents D may vary in type and scope.

The method 300 identifies context C of content D in the draft transcript106 (step 304). The context C may be identified at any level ofgranularity and distance from content D. The method 300 attempts toidentify context C in the edited transcript 110 (step 306). The method300 may identify the context C using, for example, the documentalignment described above with respect to FIG. 2A.

If the context C is identified in the edited transcript 110, then themethod 300 identifies the content E in context C in the editedtranscript 110 (step 310). Content E in the edited transcript 110corresponds to content D in the draft (original) transcript 106 becauseboth contents share the same context.

The method 300 determines whether content D and content E are equivalentto each other (step 312). The editing pattern identifier 112 may definecontent equivalence in any way. At the very least, contents D and E areequivalent if they are the same. The editing pattern identifier 112 may,however, define equivalence more broadly such that contents havingdifferences which do not constitute an error are considered to beequivalent, and therefore do not necessarily trigger the generation ofan editing pattern.

If contents D and E are equivalent to each other, then no editingpattern is generated. If contents D and E are not equivalent to eachother, the method 300 generates an editing pattern T=(D,E,C) (step 314),indicating that content D was observed to be replaced with content E incontext C. If the particular editing pattern T=(D,E,C) has been observedalready in other training documents, the method 300 may merely increasethe occurrence count N for the already existing editing pattern, therebykeeping track of how many times the editing pattern has been observed ina given training set. The method 300 repeats steps 304-314 for theremaining units of content D in the draft transcript 106 (step 316)

Note that because the method 300 shown in FIG. 3A loops over each unitof content in the draft transcript 106, the method 300 may observedifferent positive editing patterns for different instances of the samecontent. For example, the method 300 may observe not only that content Din the draft transcript 106 has been replaced with content E in contextC the edited transcript 110 (i.e., editing pattern T=(D,E,C)), but alsothat content D has been replaced with content E′ in context C (i.e.,editing pattern T=(D,E′,C)), where E′ differs from E. Similarly, themethod 300 may observe that content D has been replaced with content Ein context C′ (i.e., editing pattern T=(D,E,C)), where C′ differs fromC′. Finally, the method 300 may observe that content D has been replacedwith content E′ in context C′ (i.e., editing pattern T=(D,E′,C′)). Allof these are examples of positive editing patterns that may be observedby the method 300.

The editing pattern identifier 112 a may also generate, for eachpositive editing pattern T=(D,E,C), one or more “negative” editingpatterns of the form T=(D,D,C′) in which the same (or equivalent)content D was not edited in a context C′ that may or may not differ fromthe context C of the corresponding positive editing patterns. Referringto FIG. 3B, a flowchart is shown of a method 320 for generating suchnegative editing patterns. The method 320 enters a loop overreachexisting positive editing pattern T=(D,E,C) in the set of editingpatterns 114 a-b (referred to herein collectively as editing patterns114) (step 322). The method 320 enters a sub-loop over each occurrenceof the content D (or its equivalent) in the draft transcript 106. Itthen identifies the context C′ of the content D in the draft transcript106 (step 326) and determines whether the content D (or its equivalent)also occurs in the edited transcript 110 in the same context C′ (step328). For each such occurrence, the method 320 generates a negativeediting pattern T=(D,D,C′) (step 330).

The method 320 repeats steps 326-330 for each remaining occurrence ofcontent D (or its equivalent), and repeats steps 324-332 for eachremaining positive editing pattern (step 334).

It should be appreciated that any combination of the methods illustratedin FIGS. 3A-3B may be performed to generate any kind(s) of editingpatterns that are desired. Furthermore, the present invention is notlimited to generating the kinds of editing patterns disclosed herein.

As mentioned above in connection with FIGS. 1A and 2A, the correctionrule generator 116 generates correction rules 118 based on the editingpatterns 114. Referring to FIG. 4, a flowchart is shown of a method 400that is performed by the correction rule generator 116 to generate thecorrection rules according to one embodiment of the present invention.The method 400 begins by initializing the correction rules 118, such asby creating an empty set of correction rules (step 402).

The method 400 enters a loop over each of the existing editing patterns114, which have the form T=(D,E,C) (step 404). The method 400 determineswhether the correction rules 118 already include a correction rule ofthe form R=(D, E) (step 406).

Note that the correction rules need not be defined in terms of a mappingbetween particular content D and some other particular content E. Acorrection rule may, for example, specify a procedure to apply to aclass of contents D to produce a class of edited contents E. Forexample, a correction rule may specify that all decimal numbers bespelled out in words. Such a rule would, for example, replace “13” with“thirteen.” Such a rule may be learned by observing repeated instancesof editing patterns that are consistent with this rule.

Returning to FIG. 4, if the correction rules 118 do not include a rulethat transforms content D into content E, the method 400 adds the ruleR=(D,E) to the correction rules 118 (step 408). Otherwise, the method400 does not add a new correction rule to the correction rules 118. Themethod repeats steps 406-408 for the remaining ones of the editingpatterns 114 (step 410). Upon completion of the method 400, thecorrection rules 118 will include a correction rule for each observedtransformation of content D in the draft transcript 106 into content Ein the edited transcript 110 in the same context C.

As mentioned above in connection with FIGS. 1A and 2A, the classifiergenerator 120 generates classifiers 122 based on the editing patterns114. Referring to FIG. 5, a flowchart is shown of a method 500 that isperformed by the classifier generator 120 to generate the classifiers122 according to one embodiment of the present invention. The method 500enters a loop over each content D in the previously collected editingpatterns (step 502). As described above, the content D may be any kindof content at any level of granularity. The method 500 generates aclassifier for content D (step 504). Note, however, that the method 500may generate classifiers for any number of contents D, including asingle classifier for all of the contents D. Initially, the classifierdoes not specify any decision criteria for selecting the correction ruleto apply to content D in any context.

To aid understanding the remainder of method 500, consider an example ofthe space 900 illustrated in FIG. 9A of all possible contexts forcontent D. For purposes of example, five observed editing patterns 902a-e for content D are shown in the space 900. Editing pattern 902 aindicates that content D was observed to map to itself (i.e., to beunedited) in context C. Editing pattern 902 b indicates that content Dwas observed to map to content E₁ in context C′. Editing pattern 902 cindicates that content D was also observed to map to content E₁ incontext C″. Editing pattern 902 d indicates that content D was observedto map to content E₂ in context C′″. Finally, editing pattern 902 eindicates that content D was also observed to map to content E₂ incontext C″″. The particular editing patterns in FIG. 9A are merelyexamples.

The method 500 identifies all of the existing editing patterns forcontent D (step 506). In the example shown in FIG. 9A, the method 500would identify the editing patterns 902 a-e. The method 500 enters aloop over each correction rule R that applies to content D (step 508).In the example illustrated in FIG. 9A, the editing patterns 902 a-ecorrespond to three unique correction rules: (D,D) 906 a, (D,E₁) 906 b,and (D,E₂) 906 c.

The method 500 generates decision criteria based on features of thecontexts of the editing patterns that correspond to rule R (step 510).These decision criteria may be used by the classifier for content D todecide whether to apply the correction rule R to subsequently-observedinstances of content D based on its context. The method 500 repeats step510 for the remaining correction rules (step 512), and repeats steps504-512 for the remaining content (step 514).

As shown in FIG. 9B, the effect of the classifier for content D is topartition the space 900 into three partitions 906 a-c, each of whichcorresponds to a single correction rule. Each partition “contains” theediting patterns associated with the corresponding correction rule. Inthe current example, partition 906 a “contains” editing pattern 902 a(corresponding to the rule (D,D)); partition 906 b “contains” editingpatterns 902 b and 902 c (both corresponding to the rule (D,E₁)); andpartition 906 c “contains” editing patterns 902 d and 902 e (bothcorresponding to the rule (D,E₂)).

The purpose of step 510 is to identify decision criteria that defineequivalence classes corresponding to the partitions 906 a-c. When thesame content D is subsequently observed in a new context C* , thedecision criteria are applied to the context C* to identify thepartition in which context C* belongs. Once this partition has beenidentified, the correction rule corresponding to the partition may beapplied to the content D to produce edited content. Note that thecorrection rule corresponding to the selected partition may be theidentity mapping (D,D), indicating that content D should not be changedin context C* and that the rule does not need to be applied.

The decision criteria for each partition may be developed in any of avariety of ways. For example, features common to the contexts in apartition may be identified, and those common features used as thedecision criteria. For example, consider partition 906 b. If the word“without” appears immediately to the left of content D in both contextsC′ and C″, then “having the word ‘without’ immediately to the left ofcontent D” may be identified as a decision criteria for partition 906 b.As another example, if “Aspirin” appears in context C′ and “Prozac”appears in context C″, then the fact that there is a medication name(generalizing from the two examples to any medication name) in thecontext may be part of the decision criteria for partition 906 b.

These are merely simplified examples meant to illustrate how classifiersmight identify equivalence classes. In practice, classifiers may use anycombination of features of the observed contexts to generate decisioncriteria that define the equivalence classes. Step 510 may employ anytechniques to generate decision criteria that generalize from the commonfeatures of the observed contexts so that such decision criteria may beapplied not only to previously-observed contexts but also topreviously-unobserved contexts.

Note that the training of the system 100 described above may beperformed using more than one draft transcript 106 and correspondingedited transcript 110. In fact, the techniques described above may beusefully applied to a document corpus containing thousands or moredocuments. As the number of documents used to perform trainingincreases, the quality of the correction rules 118 and the classifiers122 will increase.

Once the error detection and correction system has been trained in themanner described above, the system may be used to detect and correcterrors in other draft documents, such as draft transcripts of spokenaudio streams, based on the contexts in which such errors occur. Ingeneral, therefore, various embodiments of the present invention may becharacterized by the method 600 illustrated in FIG. 6. The method 600enters a loop over each of a plurality of contents D in a first documentfor which it is desired that errors be corrected (step 602). The method600 identifies a context C of the content D (step 604). The method 600identifies a correction rule R, if any, that applies to content D incontext C (step 606). The method 600 applies the correction rule R, ifany, to the content D to produce corrected content (step 608). Note,however, that the correction rule R need not be applied if thecorrection rule represents the identity mapping. The method 600 repeatssteps 604-608 for the remaining contents D in the first document (step610). The result is a second document in which errors from the firstdocument have been corrected.

The method 600 illustrated in FIG. 6 assumes that a correction rule canbe selected in step 606 based on the content D and the context C.Referring to FIG. 7, a flowchart is shown of a method 700 that usesclassifiers to select a correction rule based on the current context.Referring to FIG. 8, a flowchart is shown of a method 800 that isperformed by the system 700 in one embodiment of the present inventionin which the classifiers may be used to select correction rules to applyto content based on the context of such content.

A content iterator 706 iterates over each unit of content D 708 in adraft document 702 (step 802). A context identifier 714 identifies thecontext C 716 of the content D 708 in the draft document 702 (step 804).A classifier selector 710 determines whether a classifier exists forcontent D 708 (step 806). If there is no such classifier, the contentiterator 706 selects the next content 708 from the draft document 702.

If a classifier exists for content D, the classifier selector 710selects the classifier 712, and a correction rule selector 718 appliesthe decision criteria for the classifier 712 to select a correction rule720 (from among the correction rules 118) to apply to content D 708based on the context C 716 (step 808). The correction rule selector 718may, for example, make this selection by applying the decision criteriaof each of the classifier's equivalence classes to the context 716 toproduce a score for each correction rule (with higher scoresrepresenting better satisfaction of the corresponding decisioncriteria). The correction rule selector 618 may select the correctionrule that is a member of the equivalence class having the highest score.

The correction rule selector 718, therefore, effectively uses theclassifier 712 to select the correction rule 720 by placing the contextC 716 into the best matching equivalence class of observed contexts,thereby providing the ability to generalize to previously unseencontexts. In the case of medical reports, for example, if the context Cis the text “without any signs,” it may be useful to apply the samecorrection rule as has previously been applied in a similar context,such as “without fever.” Because the correction rule selector 718selects the correction rule 720 by identifying the equivalence classwhose decision criteria provide the best score, rather than by applyingrigid rules, the correction rule selector 718 may select an appropriatecorrection rule to apply even in previously-unseen contexts.

A correction rule applicator 721 applies the selected correction rule R720 to the content D 708 to produce edited content E 722 (step 810) inan edited document 624. Note, however, that the correction rule R 720need not be applied if the correction rule R 720 represents the identitymapping. The method 800 repeats steps 804-810 for the remaining units ofcontent D 708 in the draft document 702. Upon the conclusion of themethod 800, the edited document 724 reflects the editing operationsperformed on the draft document 702 as specified by the correction rules118 and classifiers 122.

Note that the context identifier 714 may identify the context C forcontent D 708 at any level of granularity. For example, the contextidentifier 714 may be configured to identify the context for content D708 as the words immediately preceding and following content D 708, asthe sentence containing content D 708, as the author of content D 708,or as any other kind or combination of context at any level ofgranularity.

Although the correction rule selector 718 may select a correction ruleeven in the face of ambiguity about the context 716, the correction ruleselector 718 may additionally or alternatively allow a user 728 of thesystem 704 to select the correction rule to apply. The correction ruleselector 718 may use any criteria to decide whether to allow the user toselect the correction rule 720. For example, the correction ruleselector 618 may allow the user to provide a selection 730 of onecorrection rule from among competing correction rules 726 if none of theapplicable decision criteria produce a sufficiently high score or if thehighest-scoring correction rules have scores that are sufficiently closeto each other.

The candidate correction rules 726 may be presented to the user 728 inan order corresponding to an estimate of their relative likelihood ofcorrectness. The likelihood of correctness for each rule may also bepresented to the user to assist the user in selecting a correction ruleto apply. For example, if correction rule (D,E) has an estimatedlikelihood of correctness of ⅔ and correction rule (D,E′) has anestimated likelihood of correctness of ⅓, the correction rules may bepresented to the user as follows: (a) (D,E) (⅔); (b) (D,E′) (⅓).Presenting the candidate correction rules to the user 728 in decreasingestimated likelihood of correctness may facilitate the process ofselecting a valid correction rule to apply.

The system may keep track of the users choices of correction rules inparticular contexts to update its internal probabilistic model of thelikelihood of correctness of competing editing patterns (e.g., byincreasing the probabilities associated with correction rules selectedby the user). In this way, the system may learn to imitate user choicesafter a certain period of usage, at which point manual selection by theuser among alternatives may no longer be necessary.

Among the advantages of the invention are one or more of the following.Using contextual information to detect and correct errors increases thelikelihood that such errors will be detected and corrected accurately.For example, a simple context-free rule that merely replaced alloccurrences of the text “pattens” with “patterns” would fail toaccurately correct the sentence “The company owns hundreds of pattens onmedical equipment,” in which “pattens” should be replaced with“patents,” not “patterns.” Knowledge about the context of the sentence,such as the fact that it occurs in an article about the law or iswritten by a lawyer, could be used to correct such errors moreaccurately than a context-free rule. Similarly, information about thedocument section in which a word occurs or the text preceding andfollowing a word can be useful in selecting the correct editingoperation to apply to the word.

Contextual information, therefore, may be used advantageously to selectamong competing editing operations that may be used to correct an errorin a draft document. Assume, for example, that there are two editingrules that apply to content D: (D,E) and (D,E′), where E and E′ differ.In the absence of contextual information, the choice of editing rule isambiguous. The presence of contextual information, in the form ofediting patterns such as (D,E,C) and (D,E′,′C), enables a more informedchoice of editing operation to be made. If, for example, content Doccurs in context C in the current document, then editing operation(D,E) can be selected with confidence because of the matching contextualinformation contained in the editing pattern (D,E,C).

Furthermore, the present invention generalizes well to content inpreviously unseen contexts, selecting the best-matching correction rulebased on a classification of contexts into equivalence classes. Forexample, if the contexts “without any signs” and “without fever” areobserved during training, the system may generalize from these contextsto develop an equivalence class Q having the word “without” as adecision criterion. Once the system has been trained, a newly-observedcontext such as “without symptoms” will be considered a good match toequivalence class Q. The correction rule associated with equivalenceclass Q may then be applied to the new context even though it was notobserved during training.

Furthermore, the breadth and accuracy of the error detection andcorrection system disclosed herein may be improved by training it withmore documents. As more and more pairs of draft and edited documentsbecome available, editing patterns may be recomputed on larger andlarger training sets, thereby increasing the robustness of the systemwhile providing continuous adaptation to potentially changing editingbehaviors. The ability of the system to correct errors may thereforeimprove over time. In particular, when competing correction rules areobserved, the relative probabilities of the correction rules may belearned with higher degrees of accuracy by exposing the system toadditional documents.

Furthermore, the system need not be pre-programmed with particularcorrection rules because the system learns correction rules byobservation. Therefore, the system is not limited to using correctionrules that are designed by a human programmer. Furthermore, the systemmay be calibrated to work with documents in different domains bytraining it on document corpora in those domains. In this way the systemmay be configured for use with documents in different domains withoutthe need to reprogram the system.

All of these advantages lead to a reduction in the amount of time andcost required for proofreading and editing documents. The techniquesdisclosed herein may provide such reductions in cost and time either byeliminating the need for a human editor or by facilitating the job ofsuch an editor. For example, as described above, the system may flagpotential errors for the human editor and provide the editor withsuggested corrections. Furthermore, the system may be used to correctcertain errors automatically before the document is provided to thehuman editor, thereby decreasing the number of errors the human editormust identify and correct.

Detection and classification of editing patterns provides valuableinformation about what components of the draft generation process arecausing errors and how these components can be updated to improve thequality of draft documents even before applying-editing patterns. In thecase where an automatic document generation system is used to generatethe draft documents (such as the draft transcript 106), this feedbackinformation can be used to improve components of the speech recognitionand natural language processing systems that are used for documentgeneration. For instance, frequent observation of editing patternsinvolving insertion of punctuation symbols may indicate that apunctuation prediction component of an automatic document generationsystem requires attention and optimization.

It is to be understood that although the invention has been describedabove in terms of particular embodiments, the foregoing embodiments areprovided as illustrative only, and do not limit or define the scope ofthe invention. Various other embodiments, including but not limited tothe following, are also within the scope of the claims. For example,elements and components described herein may be further divided intoadditional components or joined together to form fewer components forperforming the same functions.

The invention is not limited to any of the described fields (such asmedical and legal reports), but generally applies to any kind ofstructured documents. Furthermore, the various documents used byembodiments of the present invention (such as the draft transcript 106,the edited transcript 110, and the edited document 624) may berepresented in any machine-readable form. Such forms include plain textdocuments and structured documents represented in markup languages suchas XML. Such documents may be stored in any computer-readable medium andtransmitted using any kind of communications channel and protocol.

The techniques disclosed herein may be used to perform actions otherthan error detection and correction. For example, the techniquesdisclosed herein may be applied to draft documents produced by automatictranscription systems. Such systems include an automatic speechrecognizer that associates with each word a “confidence measure”indicating the likelihood that the word has been recognized correctly.When the techniques disclosed herein are applied to a draft documenthaving such confidence measure annotations, the system may lower theconfidence measure of any content that is identified as a likely errorregion (e.g., any content D that matches the content,D in an editingpattern (D,E,C)). Such a lowered confidence measure may then trigger thecontent for review and correction.

Furthermore, different kinds (classes) of errors may be identified andtreated differently. For example, deletions of content may be treateddifferently than modifications of content, which may in turn be treateddifferently than additions of content. Misspelling of a word may betreated differently than replacement of a word with a different word.Punctuation errors may be treated differently than spelling errors.Error classification may be performed at the time of editing patterncreation or at the time of error detection. When an error is detected,the class of the error may be used to select the corrective action to betaken and/or to suggest a course of action for preventing the error inthe future. For example, the class of the error may be used to assist inimproving the (human and/or automated) transcription system 104 that isused to produce draft documents (such as the draft transcript 106). Theclass of the error may also be used to define special correction rulesthat apply to particular classes of errors.

It was stated above that each classifier is associated withcorresponding content D. The classifiers 122 may be associated withcontent at any level of granularity. For example, a classifier may beassociated with a particular word (e.g., “John”), in which case theclassifier would select the appropriate correction rule to apply to thatword depending on the context in which it appears. A classifier may,however, be associated with content at any other level of granularity,such as a sentence, document section, or even an entire document. Ineach case the classifier selects the appropriate correction rule toapply to corresponding content based on the context in which it appears.

Although certain techniques are described herein as being applied in thecontext of automatic transcription systems, this is not a requirement ofthe present invention. For example, FIG. 1A shows the use of a drafttranscript 106 and corresponding edited transcript 110 to train thesystem 100. The system 100 may, however, be trained with draft documents(and corresponding edited documents) that were not generated using(manual or automated) transcription. For example, the system 100 may betrained using documents that were written manually or that weregenerated from other documents using optical character recognition(OCR). Similarly, the draft document 702 that is corrected by thecorrection system 704 need not be a draft transcript, but rather may beany kind of document for which error detection and correction isdesired.

Although the rules 118 are referred to herein as “correction” rules,such rules are not limited to correcting transcription errors, butrather may be used more generally to perform any kind of editingoperation. For example, a correction rule may be used to edit text tocomply with a formatting requirement. Therefore, the correction rules118 more generally represent editing rules.

The techniques described above may be implemented, for example, inhardware, software, firmware, or any combination thereof. The techniquesdescribed above may be implemented in one or more computer programsexecuting on a programmable computer including a processor, a storagemedium readable by the processor (including, for example, volatile andnon-volatile memory and/or storage elements), at least one input device,and at least one output device. Program code may be applied to inputentered using the input device to perform the functions described and togenerate output. The output may be provided to one or more outputdevices.

Each computer program within the scope of the claims below may beimplemented in any programming language, such as assembly language,machine language, a high-level procedural programming language, or anobject-oriented programming language. The programming language may, forexample, be a compiled or interpreted programming language.

Each such computer program may be implemented in a computer programproduct tangibly embodied in a machine-readable storage device forexecution by a computer processor. Method steps of the invention may beperformed by a computer processor executing a program tangibly embodiedon a computer-readable medium to perform functions of the invention byoperating on input and generating output. Suitable processors include,by way of example, both general and special purpose microprocessors.Generally, the processor receives instructions and data from a read-onlymemory and/or a random access memory. Storage devices suitable fortangibly embodying computer program instructions include, for example,all forms of non-volatile memory, such as semiconductor memory devices,including EPROM, EEPROM, and flash memory devices; magnetic disks suchas internal hard disks and removable disks; magneto-optical disks; andCD-ROMs. Any of the foregoing may be supplemented by, or incorporatedin, specially-designed ASICs (application-specific integrated circuits)or FPGAs (Field-Programmable Gate Arrays). A computer can generally alsoreceive programs and data from a storage medium such as an internal disk(not shown) or a removable disk. These elements will also be found in aconventional desktop or workstation computer as well as other computerssuitable for executing computer programs implementing the methodsdescribed herein, which may be used in conjunction with any digitalprint engine or marking engine, display monitor, or other raster outputdevice capable of producing color or gray scale pixels on paper, film,display screen, or other output medium.

1. A computer-implemented method comprising steps of: (A) identifying aplurality of editing patterns of the form T=(D,E,C), wherein each of theplurality of editing patterns relates particular content D in anoriginal document corpus to corresponding content E in an editeddocument corpus in a context C shared by contents D and E; and (B)deriving at least one correction rule from the plurality of editingpatterns.
 2. The method of claim 1, wherein the step (A) comprises stepsof: (A)(1) for each of a plurality of units of content D in the originaldocument corpus, performing steps of: (A)(1) (a) identifying a context Cof content D in the original document corpus; and (A)(1(b) if the editeddocument corpus contains content E in the context C, wherein content Eis not equivalent to content D, identifying an editing pattern Trelating content D to content E in context C.
 3. The method of claim 2,further comprising a step of: (A)(2) for each of the editing patterns Tgenerated in step (A)(1), performing steps of: (A)(2)(a) identifying thecontent D and context C of the editing pattern T; and (A)(2)(b) if theoriginal document corpus contains content D in a context C′ and theedited document corpus contains content D in a context equivalent tocontext C′, identifying an editing pattern T′ relating content D tocontent D in context C′.
 4. The method of claim 1, wherein the at leastone correction rule comprises a plurality of correction rules, andwherein the method further comprises a step of: (C) deriving aclassifier for particular content D based on the plurality of editingpatterns, the classifier defining decision criteria for selecting one ofthe plurality of correction rules to apply to content D based on acontext C* of content D.
 5. The method of claim 4, wherein step (C)comprises steps of, for each distinct content E_(n) represented in theplurality of editing patterns T=(D,E,C): (C)(1) identifying a subset ofthe plurality of editing patterns for which E=E_(n); (C)(2) identifyingat least one common feature of the contexts of the subset of theplurality of editing patterns; and (C)(3) defining an equivalence classhaving decision criteria based on the at least one common feature. 6.The method of claim 1, further comprising a step of: (C) applying the atleast one correction rule to an instance of content D in a furtherdocument to edit the instance of content D in the further document. 7.The method of claim 1, further comprising a step of: (C) using contentsD of the plurality of editing patterns to identify at least onecandidate error region in a further document.
 8. The method of claim 7,further comprising a step of: (D) indicating the at least one candidateerror region to a user for review.
 9. The method of claim 8, wherein thestep (D) comprises a step of indicating to the user a plurality ofcandidate error regions ordered according to an estimate of likelihoodof correctness.
 10. The method of claim 7, further comprising a step of:(D) applying the at least one correction rule to the at least onecandidate error region in the further document to correct an error inthe further document.
 11. The method of claim 7, further comprising astep of: (D) using the plurality of editing patterns to identify a classof error in the at least one candidate error region.
 12. The method ofclaim 1, wherein the step (A) comprises a step of: (A)(1) comparingdocuments in the original document corpus to corresponding documents inthe edited document corpus to identify differences between them; and(A)(2) generating the plurality of editing patterns to reflect theidentified differences between the documents in the original documentcorpus and the documents in the edited document corpus.
 13. The methodof claim 12, wherein the identified differences comprise at least oneword that appears in the original document corpus in a particularcontext C₀ and that does not appear in the edited document corpus in thecontext C₀.
 14. The method of claim 12, wherein the identifieddifferences comprise at least one word that appears in the editeddocument corpus in a particular context C₀ and that does not appear inthe original document corpus in the context C₀.
 15. The method of claim12, wherein the identified differences comprise at least one word in theoriginal document corpus in a particular context C₀ that is spelleddifferently from at least one corresponding word in the edited documentcorpus in the context C₀.
 16. The method of claim 12, wherein theidentified differences comprise a difference in document structurebetween the original document corpus and the edited document corpus. 17.The method of claim 12, wherein the step (A)(1) comprises steps of:(A)(1)(a) aligning a first document in the original document corpus anda corresponding document in the edited document corpus; and (A)(2)(b)identifying the differences between the original document corpus and theedited document corpus based on the alignment.
 18. The method of claim1, wherein the step (A) comprises steps of: (A)(1) identifying editingactions performed on the original document corpus to produce the editeddocument-corpus; and (A)(2) generating the plurality of editing patternsto reflect the editing actions.
 19. The method of claim 1, furthercomprising a step of: (C) prior to the step (A), transcribing speech toproduce the original document corpus.
 20. The method of claim 1, whereinthe step (C) comprises a step of using an automated transcription systemto transcribe the speech to produce the original document corpus. 21.The method of claim 1, wherein the step (C) comprises a step of using atleast one human transcriptionist to produce the original documentcorpus.
 22. A computer readable medium comprising the at least onecorrection rule derived in step (B) of claim
 1. 23. A computer readablemedium comprising the at least one classifier derived in step (C) ofclaim
 4. 24. An apparatus comprising: identification means foridentifying a plurality of editing patterns of the form T=(D,E,C),wherein each of the plurality of editing patterns relates particularcontent D in an original document corpus to corresponding content E inan edited document corpus in a context C shared by contents D and E; andderivation means for deriving at least one correction rule from theplurality of editing patterns.
 25. The apparatus of claim 24, whereinthe identification means comprises, for each of a plurality of units ofcontent D in the original document corpus: means for identifying acontext C of content D in the original document corpus; and means foridentifying an editing pattern T relating content D to content E incontext C if the edited document corpus contains content E in thecontext C, wherein content E is not equivalent to content D.
 26. Theapparatus of claim 25, further comprising: for each of the editingpatterns T generated by the means for identifying the context C: meansfor identifying the content D and context C of the editing pattern T;and means for identifying an editing pattern T′ relating content D tocontent D in context C′ if the original document corpus contains contentD in a context C′ and the edited document corpus contains content D in acontext equivalent to context C′.
 27. The apparatus of claim 24, whereinthe at least one correction rule comprises a plurality of correctionrules, and wherein the apparatus further comprises: means for deriving aclassifier for particular content D based on the plurality of editingpatterns, the classifier defining decision criteria for selecting one ofthe plurality of correction rules to apply to content D based on acontext C* of content D.
 28. The apparatus of claim 24, furthercomprising: means for applying the at least one correction rule to aninstance of content D in a further document to edit the instance ofcontent D in the further document.
 29. The apparatus of claim 24,further comprising: means for using contents D of the plurality ofediting patterns to identify at least one candidate error region in afurther document.
 30. The apparatus of claim 24, wherein theidentification means comprises: means for comparing documents in theoriginal document corpus to corresponding documents in the editeddocument corpus to identify differences between them; and means forgenerating the plurality of editing patterns to reflect the identifieddifferences between the documents in the original document corpus andthe documents in the edited document corpus.
 31. The apparatus of claim30, wherein the means for comparing comprises: means for aligning afirst document in the original document corpus and a correspondingdocument in the edited document corpus; and means for identifying thedifferences between the original document corpus and the edited documentcorpus based on the alignment.
 32. The apparatus of claim 24, whereinthe identification means comprises: means for identifying editingactions performed on the original document corpus to produce the editeddocument corpus; and means for generating the plurality of editingpatterns to reflect the editing actions.
 33. A computer-implementedmethod for editing a first document, the method comprising steps of: (A)identifying first content in the document; (B) identifying a firstcontext of the first content; (C) identifying a correction rule based onthe first content and the first context; and (D) applying the correctionrule to the first content to produce second content.
 34. The method ofclaim 33, wherein the step (D) comprises a step of replacing the firstcontent with the second content in the document.
 35. The method of claim33, further comprising a step of: (E) repeating steps (A)-(D) for eachof a plurality of first contents in the document to produce a pluralityof corresponding second contents.
 36. The method of claim 33, whereinthe context comprises at least one word preceding the first content andat least one word following the first content in the document.
 37. Themethod of claim 33, wherein the context comprises a section containingthe first content in the document.
 38. The method of claim 33, whereinthe context comprises a domain of the document.
 39. The method of claim33, wherein the context comprises a work type of the document.
 40. Themethod of claim 33, wherein the context comprises an identity of anauthor of the document.
 41. The method of claim 33, wherein the contextcomprises an identity of an editor of the document.
 42. The method ofclaim 33, wherein the first content comprises text.
 43. An apparatus forediting a first document, the apparatus comprising: first identificationmeans for identifying first content in the document; secondidentification means for identifying a first context of the firstcontent; third identification means for identifying a correction rulebased on the first content and the first context; and application meansfor applying the correction rule to the first content to produce secondcontent.
 44. The apparatus of claim 43, wherein the application meanscomprises means for replacing the first content with the second contentin the document.
 45. A computer-implemented method for editing adocument, the method comprising steps of: (A) identifying first contentin the document; (B) identifying a first context of the first content;(C) determining whether a classifier applicable to the first contentexists in a predetermined set of classifiers; and (D) if the classifierexists, performing steps of: (1) using the classifier to identify acorrection rule applicable to the first content in the first context;and (2) applying the identified correction rule to the first content toproduce second content.
 46. The method of claim 45, wherein step (D)(1)comprises steps of: (D)(1)(a) identifying a plurality of decisioncriteria associated with equivalence classes defined by the classifier;(D)(1)(b) applying the decision criteria for each of the equivalenceclasses to the first context to select an equivalence class for thefirst context; and (D)(1)(c) selecting a correction rule associated withthe equivalence class selected in step (D)(1)(b).
 47. The method ofclaim 46, wherein step (D)(1)(b) comprises steps of: (D)(1)(b)(i)applying the decision criteria for each of the equivalence classes tothe first context to produce a plurality of scores indicating closenessof fit between the first context and the equivalence class; and(D)(1)(b)(ii) selecting the equivalence class corresponding to the bestof the plurality of scores.
 48. An apparatus for editing a document, theapparatus comprising: means for identifying first content in thedocument; means for identifying a first context of the first content;means for determining whether a classifier applicable to the firstcontent exists in a predetermined set of classifiers; and means forusing the classifier to identify a correction rule applicable to thefirst content in the first context and applying the identifiedcorrection rule to the first content to produce second content if theclassifier exists.